Chemistry 30

1.1 Introduction to Chemical Kinetics

The rate at which a chemical reaction occurs is often very important to us. A common task of chemists is to find ways to change the rates of chemical reactions - we want our cars and buildings to rust more slowly and our food to spoil more slowly as well. But we need the reactions that produce economically important substances, such as ammonia and medical pharmaceuticals to occur quickly.

This module investigates the key factors that determine whether a reaction will be fast or slow, and how the reaction rate may be changed. This is chemical kinetics. In order to understand how these factors affect reaction rates, you will also learn about the collision theory, the theory that helps explain what happens at a molecular level during a chemical reaction.

Key Questions

In the last unit, one of the major areas of interest was in determining whether or not a reaction would occur spontaneously. We learned that two thermodynamic factors - enthalpy (heat content) and entropy (disorder or randomness) - were key determinants of whether a reaction would actually occur or not. The speed of the reaction was not important - just whether the reaction would occur.

In this unit we are concerned with how fast the reaction occurs.  We will be asking these key questions:

• How do you measure the speed, or rate, of a reaction?
• What factors influence how fast a reaction occurs?

For example, consider how fast the reactions occur that take place in this demonstration. Also think about why the reaction slows down during the first part of the demonstration.